Sayyiduna Shaddad bin Aws (may Allah be pleased with him) narrates: I have memorized two things from the words of the Prophet Muhammad (peace and blessings be upon him): (He, peace be upon him, said:) "Indeed, Allah has prescribed excellence in everything. So when you kill, kill in the best manner, and when you slaughter, slaughter in the best manner. You should sharpen your knife and give comfort to your sacrificial animal."
(Imam Ibn Hibban, may Allah have mercy on him, says:) The statement of the Prophet (peace be upon him): "Kill in the best manner," means: when you kill in retribution (qisas), do not cause pain.